1. Field of the Invention
The present invention is directed to improvements in the air conditioning field and is directed more particularly to an improved welding pin especially adapted to fasten batts of insulation to air ducts.
2. The Prior Art
As conductive to the understanding of the present invention it should be appreciated that air conduit systems in order to minimize thermal transfer typically employ batts of insulation bonded to the interior of air ducts or conduits. Bonding is typically effected by the use of adhesives. However, adhesives alone do not reliably secure the insulation over protracted periods of time due to partial or complete rupture between the adhesive bonds, with the result that insulation may sag or fall into the air stream.
In order to assure the proper positioning of insulation it is common practice, in addition to the use of adhesives, to employ metal fasteners extending through the insulation and secured to the duct interior as by resistance welding or by impact fastening.
Welded connections have been found to provide the most reliable means of supporting insulation in the desired position. Representative examples of means for effecting welded connections may be found in one or more of the following U.S. patents issued solely or jointly to me: U.S. Pat. No. 3,624,340 of Nov. 3, 1971; 3,835,285 of Sept. 10, 1974; 3,858,024 of Dec. 31, 1974; 4,438,3l4 of Mar. 20, 1984; 4,482,795 of Nov. 13, 1984.
A problem existing in the use of welded fasteners in conjunction with the normally low density insulation materials resides in the fact that in the course of forming a resistance weld the shank of the weld pin is heated to a high temperature, with resultant damage of the insulation materials immediately adjacent the shank.
In air conduit installations it occurs that the air enters beneath the head of the attached pin and passes into the mass of insulation with a resultant billowing of the insulation.
While typical insulation batts will include a thin polymeric or metallic foil surface layer covering the fibrous insulation, the destruction of the materials adjacent the shank, in the course of applying conventional resistance weld pins,compromises the integrity of the insulation in the area surrounding the pin, with resultant disintegration of the insulating materials